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The Brain’s Growth and Development

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The human brain is large and in charge. It controls everything you do—breathing, eating, reading this sentence. Everything.

Humans have the largest brain for their body size in the animal world. Our closest relatives, chimpanzees, cannot do tasks better than an average toddler. What makes us so smart?

It’s not in the brain stem. This part controls sleeping, heartbeat, and other life-or-death activities. Our brain stem is a lot like the brain stems of reptiles, birds, and other mammals. That makes sense. We all need to do the same basic, life-or-death activities.

It’s not in the cerebellum (ser-i-BELL-um). This part controls movement. Reptiles, birds, and mammals (including us) all move. So our cerebellums are similar. But other animals use much of their brainpower for moving, sensing, and surviving. They have relatively little left for thinking.

It’s in the cerebrum. That’s a wrinkled, squishy mass that makes up 85 percent of your brain’s weight. It’s where you think and know how to talk and play instruments. It’s where you do all the things that make humans different from other animals.